[78.01] The Extent and Content of Low Ionization Gas in Galaxies

D. S. Womble (CASS/UCSD and Caltech)

The fortuitous juxtaposition of
QSOs and galaxies provides unique opportunities to probe the
extent and content of gas in the foreground galaxies through evaluation
of the incidence and strength of absorption lines in the spectra
of the background QSOs.
We present optical, spectroscopic observations of a new sample
of nine close QSO-galaxy ``pairs'';
these objects were selected with more strict limitations on the QSO-galaxy
impact parameters than in previous studies.
For a select subset of these galaxies, we present VLA
images of the H\thinspace I 21\thinspace cm emission. These
observations are combined with deep optical images and far-infrared fluxes
of the galaxies to assess and interpret morphological and environmental
conditions which may influence the absorption status.
Using these new data in combination with the existing measurements
for all pairs with similar impact parameters, we form a
``complete'' sample of 22 close pairs
from which we draw a number of global conclusions.

Naive assumptions regarding
a direct correspondence between the incidence and strength
of Ca\thinspace II absorption and the impact parameters are invalid for
these data. There does not appear to be a sharp impact parameter limit
beyond which Ca\thinspace II absorption is never detected, nor
is there a minimum
separation below which absorption is always detected.
Limits on the relative abundance of
Ca\thinspace II and H\thinspace I indicate that the
QSO-galaxy pair
absorption systems have gas-phase abundances of calcium
which are larger than
in the majority of Galactic halo sightlines. We tentatively find that
the absorbing galaxies are
more luminous in the optical and far-infrared than
the non-absorbers. Combined with a qualitative assessment of the
galaxy morphologies and environments, we find that these results are
consistent with the absorbers being characteristically more active than
the non-absorbers. Tidal interactions and active star-formation
play important and perhaps crucial roles in the origin of the
absorbing gas. We interpret these results in the
context of calcium depletion, and we briefly compare the inferred
properties with those seen in higher redshift QSO absorption systems.